It is our hypothesis that substance(s) responsible for platelet abnormalities in renal failure are dialyzed in a manner similar to "middle molecules". Patients on chronic dialysis for at least one month will be studied. Relationship between clinical stauts and blood chemistry with platelet function will be determined when dialysis flow-rate is maintained at a constant rate, when dialysis flow-rate is slowed to 100-200 c.c./minute, and during a reduction in dialysis time. If the hypothesis is correct, reduction in dialysate flow-rate should not affect platelet function, whereas reduction in time should cause platelet abnormalities.